Description
In the Linux kernel, the following vulnerability has been resolved:
ocfs2: cluster: don't sleep while holding o2hb_live_lock in o2hb_region_pin()
Patch series "ocfs2: cluster: o2hb_region_pin() fixes", v2.
This series fixes three related issues in o2hb_region_pin(), all are from
the original implementation in commit: 58a3158a5d17 ("ocfs2/cluster:
Pin/unpin o2hb regions"):
1) It is called with o2hb_live_lock (a spinlock) held, but the
underlying configfs_depend_item() sleeps (takes inode rwsem and
pins the filesystem). This triggers BUG under
CONFIG_DEBUG_ATOMIC_SLEEP.
2) When called from the configfs drop_item callback, it creates a
lock order inversion: parent inode_lock -> configfs root
inode_lock, which can deadlock against subsystem unregistration
paths taking root -> parent.
3) If pinning fails partway through o2hb_region_inc_user(), the
o2hb_dependent_users counter is leaked and partially-pinned
regions are never released, leaving heartbeat regions
unprotected on subsequent mounts.
Patch 1 reworks o2hb_region_pin() to drop o2hb_live_lock across each
sleeping configfs_depend_item() call, using a config_item reference to
keep the region alive while unlocked.
Patch 2 adds a from_callback parameter to select
configfs_depend_item_unlocked() when called from configfs context,
avoiding the inode_lock nesting.
Patch 3 fixes the error path in o2hb_region_inc_user() to unpin and
decrement the counter on failure.
This patch (of 3):
o2hb_region_pin() is always called with the o2hb_live_lock spinlock held
(from o2hb_region_inc_user() and o2hb_heartbeat_group_drop_item()), but it
calls o2nm_depend_item() -> configfs_depend_item(), which sleeps: it pins
the configfs filesystem and takes the configfs root inode rwsem. Under
CONFIG_DEBUG_ATOMIC_SLEEP this triggers:
BUG: sleeping function called from invalid context at kernel/locking/rwsem.c
in_atomic(): 1, ... name: mount.ocfs2
down_write
configfs_depend_item
o2hb_region_pin
o2hb_region_inc_user
o2hb_register_callback
dlm_register_domain_handlers
...
ocfs2_dlm_init
ocfs2_mount_volume
ocfs2_fill_super
Rework o2hb_region_pin() to pin one region at a time with the lock dropped
across the sleeping call: under o2hb_live_lock find the next eligible
region and take a config_item reference to keep it alive, drop the lock,
call o2nm_depend_item(), then retake the lock and record the pin. The
config_item_put() is done with the lock released as well, since
o2hb_region_release() also acquires o2hb_live_lock and can sleep. The
region list may change while unlocked, so the scan restarts from the top
after each pin. Local heartbeat still pins only the matching region;
global heartbeat pins all eligible regions.
The unpin path is unaffected: configfs_undepend_item() only takes a
spinlock and does not sleep.
References
